1. Field of the Invention
This invention generally relates to a high pressure fuel injection pipe often used as a fuel supply line in automobiles or other Diesel engines and a method of making the same, and more particularly to a high pressure fuel injection pipe of which the high pressure fuel flow path is formed as a smooth flow path having a uniform diameter throughout the entire length thereof including the connecting head at the end portion of the injection pipe.
2. Description of the Prior Art
In the conventional high pressure fuel injection pipe, the connecting head thereof has been plastically shaped into a frusto-conical form or an arcuate surface form with the end portion of a thick-walled, small-diametered steel pipe member being projectedly held on a chuck and by the projected portion of the steel pipe member being butt-pressed with the aid of a shaping tool.
Such conventional high pressure fuel injection pipe, however, has suffered from a problem in that, as shown in FIG. 4 of the accompanying drawings, depressions 8 with numberless hair cracks created therein are locally formed in the inner peripheral wall surface 7 of the pipe adjacent the connecting head leading to a flow path 1 when the diameter is enlarged by the aforementioned butt-pressing. Such depressions cause pulsating of the fluid to be created by the high injection pressure so that the wall surfaces of these depressions are susceptible to progressive erosion by the pressure load, with a result that outwardly directed fracture or breakage is induced in the wall of the pipe to interfere with the operation of the engine, and there is a great desire to overcome this.